In recent years, in the case of a portable terminal device such as a multifunctional portable telephone referred to as a smart phone, since a touch panel is mounted thereon as an operation input device, the number of mechanical push buttons is extremely limited, and many of them are provided with only the power-supply button for use in turning ON/OFF the power supply. Moreover, as a method for reducing power consumption, such a multifunctional portable terminal device uses a power conservation method in which switching is made between a normal power state (normal power mode) in which the power supply is not limited and a power conservation state (power conservation mode) in which the power consumption is reduced by limiting the power supply. In this case, the switching from the normal power mode to the power conservation mode is carried out on the basis of a non-operation period of time from the operation of the last time to the next operation, and when switched to the power conservation mode, the power supply to a liquid crystal device is cut-off, or the backlight of the display device is turned off so that the power consumption is reduced to the minimum level.
Moreover, conventionally, a technique has been known (see Patent Document 1) in which when switching is made to the above-mentioned power conservation mode, the power supply to a display unit is cut-off and the processing frequency of massage receipt or the like is lowered so that the power consumption is further reduced. Moreover, another technique has been known in which in addition to the display unit, the power supply to the touch screen unit is also cut-off for reducing the power consumption (see Patent Document 2).